Abstract:

The electrowetting behavior of captive bubble/oil-droplet in the surfactant solution in a low-voltage electric field is investigated experimentally. The effect of the surfactant on the electrowetting characteristics was analyzed, and the evolution of immersed bubble/oil-droplet under electric field was explored. The experimental results show that by adding N,N,N-trimethyl-1-dodecanaminium bromide(DTAB) or sodium dodecyl sulfate(SDS), contact angle reduction and bubble slip can occur in low-voltage (0 — -6 V). In addition, the increase of the surfactant concentration could reduce the voltage required for bubble slip. In a concentration of 0.05 CMC to 0.10 CMC, the captive oil-droplet in the DTAB solution presents good electrowetting performance, and the silver surface could achieve underwater superoleophobic property with θ < 30° at -3 V. Moreover, in the process of electrowetting, the contact angle and contact diameter of the bubbles/oil-droplets both gradually decrease in form of “slow-fast-slow”. The shape of the captive oil-droplet is found to be affected by the electrostatic force caused by the adsorption and charging of the ionic surfactant at the interface.

Key words: electrowetting, surfactants, contact angle, captive bubble

摘要：

对表面活性剂溶液中的浸没气泡/油滴在低压电场作用下的电润湿行为进行了实验研究。分析了活性剂对低压电润湿特性的影响，探讨了电场作用下浸没气泡/油滴形态的演变规律。实验结果表明，通过添加十二烷基三甲基溴化铵（DTAB）或十二烷基硫酸钠（SDS）活性剂，浸没气泡可在低压电场（0 ~ -6 V）作用下实现接触角减小与气泡滑移，并且增加活性剂浓度可以降低气泡滑移所需的电压。在0.05~0.10 临界胶束浓度（CMC）范围内，DTAB溶液中的浸没油滴呈现较好的电润湿特性，银表面在-3 V电压时即可实现水下超疏油特性（接触角θ<30°）。在电润湿过程中，气泡/油滴的接触角和接触直径随时间逐渐减小，并呈现“慢-快-慢”变化形式。此外，浸没油滴形态也受到离子活性剂在界面吸附带电引起的静电力的影响。

关键词: 电润湿, 表面活性剂, 接触角, 浸没气泡